1. Field of the Invention
The present invention concerns a signal transfer device for transmission of signals between two elements moving relative to one another, in particular for transfer of measurement and/or control data between a rotating part and a stationary part of a computed tomography apparatus, in which a transmission device with an RF strip conductor (stripline) on which the signals are conducted is attached on a first of the two elements and a reception device with a scanning unit is fastened on a second of the two elements, wherein the strip conductor and the scanning unit are arranged on the first and second elements such that the scanning unit moves along a longitudinal segment of the strip conductor at least during a movement segment of the relative movement of the two elements. The invention furthermore concerns a corresponding method for signal transfer.
2. Description of the Prior Art
In many technical fields large data quantities are to be transferred between elements moving relative to one another at a small distance, for example between individual apparatus parts of a measurement device. The data are normally acquired with a moving apparatus part and must be transferred to an evaluation device at a stationary apparatus part during the data acquisition. Medical imaging represents an example for such an application, and in particular computed tomography, in which a large quantity of measurement data must be transferred in real time during rotation from a rotating part of the gantry to the stationary part of the gantry. The available transfer rate represents an important criterion for the data quantity that can be transferred in real time.
Different technologies for the signal transmission between two elements moving relative to one another at a small distance are known that can be used in the field of computed tomography. In the previously most cost-effective and reliable solution, the transmission of the signals ensues via capacitive coupling from one transmitter mounted on a rotating part to an antenna arranged at a stationary part. DE 100 07 601 A1 describes a device for data transmission in which a waveguide is used as a transmitter. For the data transmission, the data are modulated on a carrier signal and injected into the waveguide. An antenna arranged in a geometrically-determined manner described in DE 100 07 601 A1 relative to the waveguide receives the carrier signal without contact so that the data are available at the stationary part after demodulation of the carrier signal. In the shown application, the waveguide is attached along the circumference of the C-arm of a C-arm x-ray apparatus and the antenna is attached on the supporting structure for this C-arm.
U.S. Pat. No. 5,140,696 describes a device for signal transmission between elements moving relative to one another, in particular in a computed tomography apparatus, in which a circular strip conductor is arranged on the circumference of the rotating part of the gantry as a transmitter and a short segment of a strip conductor is provided on the stationary part in the immediate proximity of the transmission line. The data transmission ensues in the same manner as in DE 100 07 601 A1. In these applications such strip conductors are frequently produced by a PCB technique (PCB: printed circuit board).
The continuously increasing (especially in the field of computed tomography) data quantity causes problems to be expected in the foreseeable future with this transfer technology. Modern multi-slice computed tomography system already generate data rates of many gigabits per second (Gbps). The physical bit length drops due to the increase in the data rate. The speed of the electromagnetic wave in a strip line is smaller than its speed in air, such that the bit length in the strip line is even shorter. While the receiving antenna in existing systems exhibits a length in the range of 6 to 22 cm, it must already be fashioned shorter than 2 cm given data transfer rates of 10 Gbps. This reduces the coupling capacity and therewith the signal-to-noise ratio, such that the transfer system reacts more sensitively to external interferences.
In addition to this capacitive transfer technology, individual solutions are also known for an optical transfer of the signals between the two elements moving relative to one another. For example, U.S. Pat. No. 5,535,033 discloses a signal transmission device in which a ring made of an optical waveguide is attached on the rotating part of a computed tomography gantry as a part of a transmission device that also radiates the injected light perpendicular to its longitudinal axis. The data to be transmitted are injected into this ring by modulation of the light source, and are received at the stationary part by an opto-electrical detector. Due to the annular design of the transmission device, reception of the data by the receiver is also possible during nearly every rotation phase. Optical data transfer technologies in which the signal is conducted in an optical fiber are, however, likewise limited in the achievable transfer rate due to self-phase modulation and group speed dispersion in the fiber.